1. Field of the Invention
The present invention relates to an image pickup apparatus and an image pickup method for reading out a plurality of pieces of image data having different object region sizes.
2. Description of the Related Art
Live view (LV) that is intended to observe an object, a still image of which is desired to be shot, by displaying in real time a movie being shot by an image pickup device on a display apparatus, such as a liquid crystal display, is prevalent among electronic image pickup apparatuses, such as a digital camera. When live view is in operation, a whole of an image formed on an image pickup device needs to be displayed in order to check composition. Aside from the need, there is also demand to display a precise enlarged image of a principal section in order to check the degree of focusing on a main object.
For example, Japanese Patent Application Laid-Open Publication No. 2010-226496 discloses a technique for displaying a sub-screen for a principal section enlarged image in a display screen for a whole image such that the sub-screen does not overlap with a focus AF region to avoid, e.g., a situation in which the sub-screen overlaps with a main object in the whole image.
Various techniques are proposed as examples of a technique for obtaining such a plurality of pieces of image data having different object region sizes at a frame rate suitable for LV.
An example is a technique for obtaining images having a plurality of object region sizes by changing a driving mode of an image pickup device, as shown in FIG. 13. FIG. 13 is a timing chart showing a first conventional technique which changes a driving mode of an image pickup device at constant intervals.
In the technique, a full-region LV mode of reading out an image for LV of a whole of an object region and an enlarged LV mode of enlarging only a principal section of the object region and reading out an image of the principal section as an image for LV are alternately repeated at constant intervals (intervals which are an integral multiple of a period (e.g., 16.6 ms (corresponding to 60 fps)) of a vertical synchronizing signal VD).
Another example is a technique for reading out all pixels on an image pickup device at high speed (read out at 30 fps in the shown example), converting the pixels into digital data, storing the digital data in a digital memory, and generating images having a plurality of object region sizes, as shown in FIG. 14. FIG. 14 is a timing chart showing a second conventional technique which reads out all pixels at high speed.
An image of all pixels stored in a digital memory can be used to display a whole image if the image is converted into an image for display by pixel number conversion. Additionally, an enlarged image can be obtained by extracting a desired region from the image of all the pixels stored in the digital memory and subjecting the region to pixel number conversion. Since an enlarged image is created on the basis of image data of all pixels outputted from the image pickup device in the technique, an enlarged image is not outputted from the image pickup device itself separately from a whole image.
For application of the technique as described with reference to FIG. 14, all pixels need to be read out at high speed (a higher data rate is necessary). To the end, control over driving of an image pickup device at a high frequency, readout through a plurality of channels, A/D conversion at a high frequency through a plurality of channels, and the like are necessary.